The present invention relates to alternating current (AC) driven motorized wheel assemblies that propel and retard off-highway vehicles.
In conventional direct current (DC) motorized wheel assemblies, DC motor rotors use a commutator upon which carbon brushes are held in position with brush holders attached to the motor to maintain a sliding contact and thus allow electrical power to be fed into the rotor for torque production. The brushes and commutator are high maintenance parts of the DC motor and need to be readily accessible for regular replacement and service. Therefore, DC motors are often positioned in the center of the tires with commutators at the outboard end for easy maintenance access to the brushes and removal of the rotor. Since the magnet frame of the DC motor is thick steel, it serves as both the motor frame structure and the wheel frame structure. However, locating the motor in the center of the tire limits the maximum diameter of the rotor and thus puts severe limits on the maximum power capability of the motor.
With conventional DC motors, a hollow cylinder (an axle box) provides a mounting structure for the wheels and serves as an air plenum for cooling air for the wheel motors which originates from remote blowers and exits through the wheels.
It is therefore seen to be desirable to have a motorized wheel assembly for propelling and retarding off-highway vehicles with lower costs and maintenance requirements. An AC induction motor transfers electrical power to a rotor via electrical induction and therefore needs no commutator or brushes. As compared with a DC motor, an AC motor requires much less maintenance and therefore can be placed in a location where frequent access is not necessary. The cost of the AC motor can be minimized by using a rotor diameter which is as large as possible. In a preferred embodiment of the present invention, AC motors are moved inboard into the axle box where cooling air is available and the diameter of the motor is no longer as restricted. The transmission (which in one embodiment includes a double reduction gear unit) is placed outboard of the tires with a shaft connecting it to the motor allowing the hub diameter and hub bearing diameters to be minimized. Since the limit on motor diameter has been relieved, a higher power capability motorized wheel can be provided with a lower maintenance motor.
With the location of the motors and the transmission in the present invention, air cannot pass through the wheels because the transmission blocks the outlet. Therefore, another method of cooling the motors is needed. The structural integrity of the axle box is very important because the axle box supports two-thirds of the truck""s weight and all of the torque reaction. Adding additional air outlet holes or performing any other modifications can affect the structural integrity of the axle box.
In one embodiment of the present invention, air holes are provided in flanges supporting the motor so that cooling air (which enters the axle box from an air inlet duct) can enter the motor from the outboard side and exit the motors into the center of the axle box before being ducted out through an existing service access opening in the rear of the axle box. In this embodiment, the motors can be cooled without adding additional holes to the axle box. Thus, by using the air inlet duct and service access hole in the axle box which already exist for DC motorized wheels, the present invention does not affect the axle box structural design and thus does not create a risk of weakening the structural integrity of the axle box.